An intake/exhaust valve mechanism of an internal combustion engine is provided with a valve stem seal that seals a gap between a valve stem and a valve stem guide. Generally, a valve stem seal is constituted by a reinforcing ring which is fixed to a valve stem guide and a seal main body made of an elastic body which is attached to the reinforcing ring by integral molding or the like. A technique is known in which a reinforcing ring is further provided with a locking protrusion to be locked by a locking recess provided on a valve stem guide. An example of this technique will be described with reference to FIG. 3. FIG. 3 is a partial breakaway sectional view showing a state during use of a valve stem seal according to a conventional example. Moreover, FIG. 3 shows a vicinity of where the valve stem seal is provided in the intake/exhaust valve mechanism. In addition, FIG. 3 shows a state where a part of a left side of the drawing has been broken away.
The intake/exhaust valve mechanism is provided on a cylinder head 200. In addition, the intake/exhaust valve mechanism includes a valve stem 300, a valve stem guide 400 which guides movement in an axial direction of the valve stem 300, a spring 500 for closing a valve, and a valve stem seal 700 which seals a gap between the valve stem 300 and the valve stem guide 400.
The valve stem seal 700 is constituted by a reinforcing ring 710 made of metal or resin, a seal main body 720 made of an elastic body which is attached to the reinforcing ring 710 by integral molding or the like, and a garter spring 730 which presses the seal main body 720 toward a side of an inner circumferential surface. In addition, the reinforcing ring 710 is provided with a locking protrusion 712 to be locked by a locking recess 410 that is provided on the valve stem guide 400. In this conventional example, as shown, an inverted U-shape slit 711 is provided on the reinforcing ring 710. In addition, the locking protrusion 712 is formed as an inner-side portion of the slit 711 is folded radially inward. A tip of the locking protrusion 712 abuts against a side surface 411 of the locking recess 410 to prevent the reinforcing ring 710 from detaching from the valve stem guide 400.
However, the locking protrusion 712 according to the conventional example does not have sufficient structural strength. Therefore, when pressure inside a sealed space K formed by the valve stem 300, a tip of the valve stem guide 400, and the seal main body 720 rises, there is a risk that the tip of the locking protrusion 712 is pushed forcefully, causing the locking protrusion 712 to break. Accordingly, the seal main body 720 may detach from the tip of the valve stem guide 400 and sealing performance may be impaired.
Furthermore, in another known technique, two slits extending linearly in a circumferential direction are provided on a reinforcing ring and a locking protrusion is provided by folding a portion between the slits radially inward (refer to Patent Literature 1). With this technique, even though strength of the locking protrusion can be enhanced, there is a problem of low workability due to the likelihood of the locking protrusion getting caught by a tip of a valve stem guide when mounting the reinforcing ring to the valve stem guide.